Method of forming a bend in ductile metal tubing



METHOD OF FORMING A BEND IN DUCTILE METAL TUBING Filed Jan. 2, 1952 .h me 5, 1956 c, DRAPER ET AL 7 Sheets-Sheet l June 5, 1956 F. c. DRAPER ET AL 7 2,748,455-

METHOD OF FORMING A BEND IN DUCTILE METAL TUBING Filed Jan. 2, 1952 7 Sheets-Sheet 2 w n w a m r 0 m. M t H mm A M K W 1.1L 0 1. M k. *2 v n y Ai B 3mm F3 June 5, 1956 F, c. DRAPER ET AL 2,748,455

METHOD OF FORMING A BEND IN DUCTILE METAL TUBING Filed Jan. 2, 1952 7 Sheets-Sheet :s

V B aw WM w,

Attorney June 5, 1956 F. C. DRAPER ET AL METHOD OF FORMING A BEND IN DUCTILE METAL TUBING Filed Jan. 2, 1952 7 Sheets-Sheet 4 WWW 1 ($341 A Home y June 5, 1956 F. c. DRAPER ET AL 2,748,455

METHOD OF FORMING A BEND IN DUCTILE METAL TUBING 7 Sheets-Sheet 5 Filed Jan. 2, 1952 Ql'lllllllllllllllllllIllIIlll I Ill);

A ltorne y June 5, 1956 c, DRAPER ET AL 2,748,455

METHOD OF FORMING A BEND IN DUCTILE METAL TUBI-NG A Home y June 5, 1956 F. c. DRAPER ET AL 2,748,455

METHOD OF FORMING A BEND IN DUCTILE METAL TUBING Filed Jan. 2, 1952 7 Sheets-Sheet 7 (I IIIIIllllllIIIIIIIIIIIIIIII'II IIIIIIIIIIIIIIIIIIIIllllIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIII IIIIIIIIII Inventor B nu; YWM, Attorney United States Patent." Ghee 2,748,455 Patented June 5, 19,56

METHOD OF FORMING A BEND vIN .DUCTILE l METAL TUBING,

Frederick CecilDraper and John Frederick H'obson, Edg-- ware, England, and William Sang, t Toronto, Ontario, Canada, assignors to Boosey 85. Hawkes, Limited, Edgware, England, a- British company,

Application January 2; 1952, Serial No. 264,418

Claims priority, application GreatBritainJanuary'S;1951:

6 Claims. (Cl; 29-157.6)

This" invention relates-to the formationof bends in tubing made. of' d'uctilemefal and is :particularly concerned with the treatment of such tubing in which" the diameter is large'in'relation to the ,wall thickness. The invention thus has particular application inconnection with the production of" musical, Wind instruments; the main body of" which consists of a: metahtube having one or more bends in it: The customary =way; of 'producing the necessary shapeirr a tube for awindinstrunrent-of this kind is to start with a sheet metal blank from-which the tube is shaped and then to bendthetubemanually in ax large-number of small stages;

When bending a tube in this-way, a bending moment is appli'edto the tube; u'sual-l'y in theform of'opposing forces acting on theexternal' walls, sothat asthe tube bends; a-neutral axis :is establishedpassing approximately through the centre-of gravity of the tube; Thus'all: the parts of the wall 1 of the tube-lying on one" side of this neutral axis-are-subject=to tension; while parts on the other side are-subjectto compression. Non/"although the material of the *tube merely elongates und'entlie action of tension, the eifect of the compression is tomausethe thin wall 'to buckle and collapse; The amounoof compressioirwhich can be sustainediby the thin wall ofthe tube which thus -acts asa--strut-= is' very-small; and: the result is that as soonas a bending rnoment:is applied to the tube, small wrinkles appear on th'e insideofi thezbend where the compressionis exertedf In the ordinary procedure; therefore, these wrinkles: on cockl'es-" have-to: be beaten out Iby hand, after whiehsthe tube is annealedend' then bent azifurthersstagea. I'naorder to-obtain ther-finaldesired degreevoff blending a large number of 'steps ofi alternate: bending andi beatingstogether with intermediat'er annealingearewequiredgu andithe process as such is very lengthy;

0116 manner in: which sucl'tacoclclingsofi therwalk-ofi the tube which lies on the: inside ofrithe:hendaicanrtberavoidedg is to applyabending:momentetmthe'tubwwhileinofi setting up any appreciable" compressive? Stl'ESSCSE. in the:. walla. Various: proposals: have been: madeza ini orders to! achieve these; conditionsaand, although in: ,practiceqsome ofi' them have been successtuhwith: relatively smalla diameter; piping, .,conside-rable d-i-fiiculty inexperienced inrdealing with large diameter tubing.;with thinnwalls where the-ratios, of the diameter torthe: wall. thicknessris, K greater, than about thirty. five. totoner Tubing ofthiscgeneral class has a variety of uses in industry such as large bOIe" ShOI'f elbows for petrol and oil'tanks in. aircraft, ducts, particularlyfor' aircraft and, power-boats, and also as fuel and secondary air distributing rings on" gasturbines and a satisfactory process for bending tubing of this kind haslongbeen-requiredt According to the present invention; a length-of tubing whiclris to be bent is-fi'rst' compressed laterally-so as to cause the parts of the wall which are to constitute: the inner and outer surfaces of the bend respec-tively to ap proach" one another to gi-veashape ofi tube-whiclfi when seen in-cross=sectiorr isscon'cave towards the side which is to constitute the outside of the bend; after which'.the tube is pressedtinto contact with. a former to give it the desired curvature in an axial" direction, preferably; by means of a roller turning in an. arm pivotedlaflth'e centre of curvature. The effect ofthis'.operation is to cause, the compressed tube to behave in a.manner similar to a thin strip, the two opposing walls' whichhave been brought close to one anotherbyth'e compression being pressed into contactwith one. anotherby the roller and bending together to conform to the shape'of the former. Thus the wall which is toconstitutetheinsideofthe bend and which would normally: cockle owing to' the setting up of compressive stressesis'bentsrnoothly'byabending' moment which sets up a neutral axis passing througlrthe material of the wall'itself, thujstreducin'g-compression to" a negligible amount: Thebent; compresseduube is finally enclosed within a die havingan interior shape-cone; sponding to the required"external contour of the tube and fluid, pressure is applied toforce the wall: outwardly 'so as to expandthetube to the desired final shape:

The tube should 'be anchored-Within the-die so 'thattheinner radius of'the'bendfits snugly'tcrfhe wallof the-die and'in amannerwhich prevents-tho tub'efronrmovingforwardundertlre-applied= fluid pressure; The applicationoffluid pressure to the-inside-of the tubestretch'es the material uniformly under the predominantly tensile radial stresses and providedthednner radius of the-tube is properly-fittedto the die and 'securely. held; there is no tendency foncompressive-stresses-1o develop err-the inner radius of" the bend and the dangeroft welding is therefore eliminated In order to \al-low for thetreadyinsertion of the tube in the die,v a split die consisting--ot two 'halves may-be used, and in order'that thebent tube -shall fit snugly inthe lower half of the diear-before 'the die is closed, it is preferred that the tubing should be-compressed to an approximately semicircular or U' shapecl configuration when seen in cross-section; In other words; the portion of the wall t or the-tubewhicli: is to coustitute the inside ofthe-bendis' allowed to-retain-its= original curvature; whilethe otherportion 0:5 the wall of the: tube iswcoma pressed'inwardl y into-contact withv the first portion so that i the final shape of the: compressed itubewiss that of: an elongated trough.

The application of fluid pressure in the dievhasilittle effect Otlsfllfii portions of thee-wall which isptovformuhe inside of: the bend sin'cetthisistclosely suppoeted:.the wall of the die.- The: principal effect;- oithe. application of pressureis-firstly:foreverse the CULVHtLIIIELOfTth6 remains ingportion of the: wall andithenutorstretch itxandiforce it into". contact withthe further. wall" of the: die; This stretching pro'cessiinvolves aihighidegreerofifcoldsworking of the metal. of the tubezand it ispreterable tocarry it out in twostages. In the;firstistagerjust"sufficientapressure is applied to reverse the: curvature of titer-concave portion of the walll and:to carryoutia smallsinitiali degree of stretching. After-thisxtheltube is removed'rfrom: the :die and: annealed, andithen the-final stretching operation is completed; The; otherstepsrin; the; process, namely, the initialcompression; follbwed'sby the :bendi'ng, ,ElSQElIIVQll/C a high degree: of cold'eworking;.anththeser steps also; therefore, must usuall'y befollowed by an annealing; treatment;

A. process) for-bending: a; tube-in accordance: with the invention will nowabezdescribed' in morerdetail-t by way ofzexample with reference; to the'accompa-nying draw: ings,. in" which:

Figures 1 to 4 show successive stages in the: treatment of the tube;

Figures 5;. and 6-'illustrate;diagrammatically the initial step, of compression 10f :1 thertube;

Figurea7 isamplan view of; former, illustratingathc method: ofi'bendingetlie compressed: tubc;.

Figure 8 is a cross-section on the line V1II-VIII in Figure 7;

Figure 9 is a perspective view of a split die in the open position with a bent tube in position in the lower half;

Figure is a plan view of the lower half of the die shown in Figure 9 with part of the tube in cross-section;

Figure 11 is a part-sectional view on the line XIXI in Figure 10 showing the cross-section of the compressed tube in the die; and

Figures 12, 13 and 14 are diagrams of the hydraulic circuit used in conjunction with the die.

The principle employed in accordance with the invention is best appreciated from Figures 1 to 4, which show the successive stages in the shape of a tube or pipe under treatment. A plain length of pipe or tubing 1, as seen in Figure 1, is first compressed to the shape shown in Figure 2 so as to cause the walls of the ,tube, which are to constitute the inside and outside portion of the bend respectively, to approach one another over a length 2, which is to constitute the bent portion. The compressed portion of the tube is approximately semi-circular or U-shaped in cross-section as may be seen in Figure 2 and also more clearly in Figure 11. The compressed tube is then bent axially to the desired curvature, and Figure 3 shows the tubing of Figure 2 bent through a curve of 180 degrees. Finally, the bent, compressed tubing of Figure 3 is expanded by hydraulic pressure in a die to the final shape shown in Figure 4.

The initial operation of compression is carried out in a mechanical press, the tubing 1 being placed in the female member 3 of the press, shown diagrammatically in Figure 5, where it is compressed by the male member 4 in the manner shown in Figure 6.

After annealing, the compressed tubing, in the shape shown in Figure 2, is then treated on the former shown in Figure 7. This former is made of hard metal and has a contour 5 corresponding to the desired shape of the bend, in this case a semi-circle. In addition, the forming edge has a concave profile 6, as seen in Figure 8, for the reception of the convex face of the compressed tube. Pivoted at the centre of curvature of the semi-circular contour 5 by means of a removable pin 7 is an operating lever 8 comprising spaced side members 9 between which is mounted a pressing roller 16 turning in a spindle 11. This roller has a convex profile 12 for co-operation with the concave profile 6 of the forming edge 5.

One end of the compressed tubing is gripped in a chuck 15 so that the tubing extends along one side of the former in the position shown as 1a, with the end of the compression portion 2 coinciding approximately with the beginning of the semi-circular contour 5. The operating lever 8 is next placed in the position shown as 8a with its side members 9 straddling the tubing, and the pin 7 is inserted. The roller 10 thus engages the end of the compressed portion 2. The operator then swings the lever 8 about the pivot pin 7 and the tubing 1 is bent to the desired shape. An intermediate position of the lever 8 is shown at 811, in which the tubing has been bent to the shape 1b. When the operation is complete, a semicircular bend has been formed in the tube. As will be best appreciated from Figure 8, the cooperation between the profile 12 of the roller and the profile 6 of the former is such as to set up a bending moment with a neutral axis passing through the material of the wall of the tube. Thus compressive stresses are reduced to a very small value, and in addition the rolling action prevents the formation of any cockles, so that the tube behaves virtually as a thin strip.

The bent tubing is then annealed and is inserted in the lower half 19 of a split die made of white brass, and

supported on a pedestal 20 as seen in Figures 9 and 10. One end of the tubing is plugged by means of a plug 21 provided with a sealing ring 22. The outer wall'of' the tube is gripped by a split bush 23, which serves to lock the plug 21 in position. The plug 21 is formed with an enlarged head 24 which fits into a corresponding recess in the die 20 and serves to lock this end of the tube firmly in position. At the other end of the tube, a hydraulic fluid inlet valve 25 provided with a sealing ring 26 is inserted and locked in position by a split bush 27, which serves to anchor this end of the tubing also. With both ends anchored in this manner, the inner face of the tubing is held snugly against the corresponding face of the die, and all tendency to cockle is avoided. The cross-section of the tube in the die is shown in Figure ll, from which the close fit and the nature of the deformation of the outer wall necessary to force it into the position shown by the dotted line is clearly seen.

When the tube is in position in the lower half of the die 20, the upper half 30 is lowered into position, moving on guides 31 under the action of hydraulic pressure applied by a cylinder 32. To start the operation necessary to expand the tube, hydraulic fluid under low pressure is first introduced by way of a connecting pipe 32 connected to the inlet valve 25. In order to bleed off the air contained in the tube, the plug 21 is formed with a narrow passage 33 provided with a petcock 34, fitted with a length of rubber tubing 35 which serves to drain off any fluid which may be expelled during the bleeding process.

As soon as the bleeding is complete, the cock is closed and the pressure of the hydraulic fluid is increased to a value such as to bring about the initial expansion of the tube. After this the pressure is removed, the tube re moved from the die and annealed. It is then returned to the die for the final operation of expansion. One end is plugged and gripped by the plug 21 and the split bush 23 as before, but the other end, in which the pressure valve 25 is inserted, remains free to slide in the die, by replacing the split bush 27 with a round bush which is a sliding fit. The full hydraulic pressure is then applied to the inside of the tube and serves to expand the wall on the outside of the bend into contact with the wall of the die. This expansion may require a short extra length of the tube to be drawn into the die and it is for this reason that one end is left free. When the tubing has been finally expanded, it is removed from the die and once again annealed. The ends of the tubing which have been gripped in the die are cut off and then after a final surface treatment, such as bufling, the tubing is ready for use.

The method of obtaining the necessary hydraulic pressure both for expanding the tube and for operating the top half 30 of the die, which acts as a vice to grip the tube, is illustrated diagrammatically in Figures 12, 13 and 14.

In practice, the hydraulic fluid used is water having dissolved in it a small quantity of soluble oil sufiicient to prevent corrosion of the working parts. This is supplied at a relatively low pressure in the region of lbs. per square inch at 50, and this low pressure is employed for opening and closing the vice. The high pressure required for expanding the tubing is obtained by the use of an intensifier 51 comprising pistons 52 and 53 connected together by a rod 54 and acting in opposition to one another. The piston 52, which may have an area ranging between about thirty and a hundred and twenty times that of the piston 53, is acted on by compressed air also at a pressure in the region of 100 lbs. per square inch, which is admitted to the system by way of a pipe 55. The pressure exerted by the piston 53 on the water in contact with it is therefore greater than that of the compressed air in the ratio of the areas of the pistons 52 and 53, and for the ratios given above will range between about one and a half and five tons per square inch according to the work to be carried out. The operation of the system is controlled by means of a valve box indicated generally at 56 and comprising six positively seating poppet valves, which are cam-operated and which give emssa the three changes ofci'rcuit required by rotating a handle controlling the cam insteps of; 120 degrees.

In the position-of thevalves shown-in FigurelZ, the tubing has justbeen inserted in the'lower half 20 ofthe die and the viceis'in the process "of being' closed. The low pressure water enteringthe system at 50.(indicated by transverse shading) passes first through a non-return valve 60. Passing by way of a pipe 63, low pressure water is in contact with the upper surface of. the piston-.53, which is in its lowest position. Thelow pressure water also passes. by way of a pipe 65 through another of; the poppet:valves 66 and thence via afpipei. 67 to actaon the upper surface of a piston 68 working irrthe cylinder132 and controlling the closing of the vice; In addition, the low pressure water. passes by way. of a pipe 69 and an isolating valve 70"to fill a length oftubing under treatment at 71 As soon as the vice is completely closed and all air has been bled from the tubing, the valves are moved into the position shown in Figure 13. In this position, compressed air entering the system at 55 (indicated by longitudinal shading) passes by way of a pipe 75, a pressure-reducing valve R and a pressure gauge G, through a further poppet valve 76 and thence via the pipe 62 to the underside of the piston 52. The upper side of the piston 52 is connected by way of a pipe 77 through one of the valves 78 to exhaust at 64 (indicated by broken longitudinal shading), and in the same manner the underside of the piston 68 is also connected to exhaust by way of the pipe 79.

The action of the compressed air pressure on the underside of the piston 52 applies high pressure to the water in contact with the upper side of the piston 53 (indicated by crisscross shading). This high pressure is transmitted along the pipe 61 and thence via the valve 66 and the pipe 67 to the vice and also to the tubing at 71, being prevented from passing back to the supply by the presence of the non-return valve 60. This high pressure firmly clamps the vice and at the same time expands the tubing in the die.

When the expansion is complete, the valves are moved to the position shown in Figure 14, relieving the pressure on the tubing, and at the same time opening the vice. In this position, the compressed air is cut ofi? from the lower side of the piston 52, which is then connected to exhaust via the valve 53. Movement of another of the valves 80 applies the compressed air to the upper side of the piston 52, returning it to the bottom of its stroke, and also by way of the pipe 79 applies pressure to the underside of the piston 58, thus opening the vice. At the same time, movement of a valve 81 connects the water acting on the top of the cylinder 68 and on the tubing at 71 to exhaust (as indicated by the broken transverse shading). This removal of the pressure from the top of the piston 68 allows this to move upwardly under the action of the compressed air acting on its underside, so as to open the vice. Similarly, the removal of the pressure from the tubing allows this to be disconnected with safety. It can then be further isolated from the source of pressure by means of the valve 70.

The actual pressure of the high pressure water is governed by that of the compressed air in the intensifier and hence by the setting of the reducing valve R. Thus for the first stage of this expansion, the reducing valve R is set to give a value of the pressure just sufficient for reversing the curvature of the wall of the tubing which is to form the outside of the bend, and the cycle of operations just described is then carried out. After the tubing has been annealed, it is reinserted in the die, the valve R is adjusted to give full pressure and the cycle of operations is repeated to complete the expansion of the tubing.

In the manufacture of musical instruments, the tubing which is to be bent is seldom of uniform bore and usually tapers from one end to the other. The introduction of a taper into the tubing has further complicated matters when producing the tubing by hand as previously described? Wlien using the method in accordance with the invention, however; ordinary parall'el tubing'may be the desired" taper and the final. expansion stagethenexpandsthe" tu-bingtogiveit a; corresponding taper:

Moreover thebend ingthe tubing need not necessarily be in-the shape of 'a circular-arc. The forming; edge 5 may haveanygdesired'shapiz forexample parabolicor' hyperbolic. Insuch-cases, of course, theoperatinglever 8'cannot be-simply pivoted but must-serve to move the roller round a, correspondingly shapedguide track. The split? die must naturally also; conformto the" curve in question:

As alreadvrnentioned; the method just' described is particularly useful in the manufactureof musical instruments: The results obtained in'this'way are" far-superior and more uniform than those obtained by means of the previous methods of hand bending and, by this method, for the first time it has proved possible to manufacture the large bore branches and bends of sousaphones, basses, tubas, euphoniums and similar bass instruments from ordinary seamless brass tubing.

Although the problem has been dealt with primarily in its application to the manufacture of a musical instrument, similar problems arise in other branches of industry in which pipes having a large diameter in comparison with their wall thickness are required to be bent. This method is particularly useful in bending such pipes made of brass or other ductile metals such as any of the Well-known light alloys.

We claim:

1. A method of forming a bend in a length of tubing of ductible metal comprising the steps of supporting one side of said tubing and compressing its opposite side laterally so as to cause the parts of the wall of said tubing which are to constitute the inner and outer surfaces of the bend respectively to approach one another toward the inner side of said tubing, whereby the cross-section thereof becomes concave towards the side which is to constitute the outside of the bend, bending said tubing progressively along its axis around a concave former to the desired curvature, said bending being carried out by rolling pressure on said concave outer side so as to minimize causing compressive stresses in the metal of said tubing, and expanding the concave side of said tubing outwardly to the desired final shape.

2. A method of forming a bend in a length of tubing, as claimed in claim 1, in which the cross-section of said compressed concave length of tubing is approximately semi-circular.

3. A method of forming a bend in a length of tubing of ductile metal, comprising the steps of compressing said tubing laterally to give a U-shaped cross-section, rolling said compressed tubing into contact with a concave former of the desired curvature, the convex surface of the bottom of the U during the rolling step being in contact with the former so as to constitute the inside of the bend, and applying fluid pressure to the interior of said tubing, said tubing during said final step being enclosed in a die corresponding to the desired final shape of said tubing.

4. A method of forming a bend in a length of tubing of ductible metal, comprising the steps of compressing said tubing laterally to collapse one side and form a substantially semi-circular concavo-convex cross-section, annealing said tubing, rolling said tubing longitudinally of said collapse-d side to force its convex side into con tact with a former of the desired curvature, again an-- nealing said tubing, enclosing said tubing in a die cor-J responding to the desired final shape of said tubing, applying relatively low hydraulic pressure to said tubing while enclosed in said die, again annealing said tubing, applying greater hydraulic pressure to the interior of said tubing while enclosed in said die sulficient to force the 7 walls of said tubing into contact with the walls of said die, and finally annealing said tubing.

5. A method of forming a long bend in a length of thin-walled tubing of ductile metal comprising the steps of laterally compressing and inwardly deforming a side thereof adjacent to the opposite side to collapse said tube into concave approximately semicylindrical shape for a substantial portion of its length sufficient to form the desired bend, rolling said deformed tubing along its axis around a peripherally grooved former while maintaining its convex side in stationary contact with the groove in said former to stretch its outer edges and prevent forming cockles in its convex side, and applying fluid pressure to the interior of said deformed bent length of tubing to expand and stretch the same to smooth tubular bent form.

6. A method of forming a tapering bend in a length 8 of cylindrical tubing as set forth in claim 5 wherein the deformed portion is annealed prior to the bending and the expanding steps, and the final expanding step is performed under high pressure in a hollowaxially tapered die to shape the tube to conform to the die.

References Cited in the file of this patent UNITED STATES PATENTS 169,392 Wicks Nov. 2, 1875 1,210,629 Foster Jan. 2, 1917 1,542,983 Bergmann June 23, 1925 1,714,989 Schlaich May 28, 1929 2,285,275 Harder June 2, 1942 2,500,813 Fritsch Mar. 14, 1950 FOREIGN PATENTS 624,227 Great Britain May 31, 1949 

